In November and December, a polynya (area of reduced ice concentration surrounded by heavy pack ice) usually develops on the western Ross Sea continental shelf immediately north of the Ross Ice Shelf. This important regional feature is reasonably well simulated by the Universit¿ Catholique de Louvain (UCL) global ice-ocean model, despite its coarse resolution. The model results suggest that both the wind-induced divergence of the sea ice and the inflow of relatively warm Circumpolar Deep Water (CDW) onto the continental shelf are essential for the polynya formation, which supports the inference drawn from observational data. ¿ 1999 American Geophysical Union